A gear set has a module of 5mm, a 20° pressure angle, and a 24-tooth case-iron spur pinion driving a 48-tooth case-iron gear. The pinion is to rotate at 50 rev/min. What horsepower input can be used with this gear set if the contact stress is limited to 690 MPa and F=60mm? Use the first approximation equation for contact stress, not the AGMA equations.